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"Ringing from pre-amp

I just swapped out the Sovtek 6922s from my BAT VK3i pre with 4 NOS Siemens E88CCs. I did NOT replace the 2 Sovtek 6V6s. After about 4-5 hours of use, the pre has developed a significant "ringing" sound, a steady pitch tone that cuts out when I mute the output. It is not a hum, but a clear tone like you would hear if you struck a crystal wine glass. It is not present immediately after the mute-on-start delay kicks out, but appears within a few minutes thereafter. It is loud enough to be heard distinctly in the background with moderate level music and is quite noticable without any volume. I also notice a significant level of what I will call microphonics (when you tap the top of the case without any input (but not muted), it produces a sound thru the speakers. It occurs most prominently when you tap the case over the 6v6s. The unit is also running warmer than before. The sound, however, it more detailed and little more forward, with excellent bass. I did not get a chance to contact BAT today. I would also note that also I recently installed a BAT factory phono card. Any help would be most helpful. I am not an experienced electronics tech or only moderately handy. I do not have a nearby BAT dealer.
128x128swampwalker
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swampwalker OP
5,138 posts
 
Bob- do you think its one of the signal (EC88) tubes, or could the new signal tubes have overloaded one of the drivers (6v6). I hope its not one of the EC88s; I just bought them from a guy in Singapore and they are marked as matched, tested quad, with measurements. Even tho I've owned tube or hybrid products for many years (starting with a NYAL Moscode 300) I'm really a neophyte with the tube details, I'm not sure I even have the terms correct.
bob_bundus
1,834 posts
 
I'm not that well versed with glassware myself Swamp. The 6V6's are output followers or buffers? Whatever, doubful that anything has been damaged. After you run the "tap-test" revert to your original tube configuration in order to find out for sure. In my case the ringing tube was in the gain stage, not the output. If it's possible to swap tubes around, then try that too as a diagnostic tool, even if it temporarily un-matches them. Your seller may not have experienced this problem because tubes' behavior can vary depending upon the circuit design of the equipment that they're used in. That, or you were taken? You might also discuss this issue with the seller?
swampwalker's avatar
swampwalker OP
5,138 posts
 
Well now you've gone way beyond my knowledge of circuitry. Have no idea what an output follower or a buffer is. I can and will try the tap-test as soon as I get some time (pulling out the 16 torx screws from the BAT time after time is a real hassle). I hope that its not a problem with the NOS tubes since I fear that international customer service is not a strong point of ebay auctions.
lphunter2
15 posts
 
You should never tap tubes, you can ruin a tube real quick that way. Check out TUBE BASICS AND FREQUENTLY ASKED QUESTIONS on Upscale Audio's website @ www.upscaleaudio.com.
massvm
126 posts
 
Without knowing why it worked, let me provide a possible solution that was recommended to me and was successful. I had a similar ringing on one channel of my Line-3 when I put in 7308s, and it was recommended that I swap the channels they were being used in. It worked. No more ringing. Try changing the position of the E88 tubes ... seems like an easy fix and a heck of a lot easier than trying to get your money back.
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